1. Field of the Invention
The present invention relates to a method for releasing a connection in a two-layer communication network.
2. Description of the Prior Art
As used herein, a two-layer communication network means a communication network comprising a first communication network layer adapted to establish or which establishes a communication channel to a terminal communicating in a call and transmitting the call, and a second communication network layer adapted to establish or which establishes the call. An application layer as used herein means a set of security mechanisms, files, data and protocols (excluding transmission layer protocols). A call as used herein means a logical association between at least two users. A communication channel as used herein means a logical connection in the transmission layer between at least two end-points (for example between a mobile terminal and a support node). Of course, the present invention is not limited to voice calls, but the expression call is intended to represent a subset of sessions.
A terminal may be any communication end-point which is adapted to send or which sends and/or adapted to receive which receives data via a communication channel. In particular, a terminal can be a wireless terminal, or a terminal communicating via wires. Examples of terminals are radio terminals also referred to as a mobile station MS, or a user equipment UE (terminal conforming to UMTS standards also known as third generation (3G) terminal), or a server device.
FIG. 1 shows an example of a basic network architecture for a two-layer communication network. The illustrated example is given with reference to a UMTS/GPRS network as a first communication network layer adapted to establish or which establishes a communication channel to a terminal (UE) communicating in a call and transmitting the call, and an Internet Protocol based IP network as a second communication network layer adapted to establish or which establishes a call (for example Internet Protocol Telephony IPT). However, networks operated according to other standards may be chosen while the applicability of the present invention will not substantially be influenced thereby.
A user equipment UE as a terminal communicates with and/or via the communication network. This means that the user equipment UE may communicate with another user equipment (not shown) or with a server entity (not shown) within or external to the communication network. An external server entity could in turn be regarded as a terminal. The party initiating the call is referred to as the caller, while the called party is referred to as the callee. The communication network shown in FIG. 1 is a two-layer communication network consisting of a GPRS/UMTS network as an example for a first communication network layer, and of an Internet Protocol based (IP) network as an example for a second communication network layer. Between the first and second communication network layers at least one interface I/F is present. In the illustrated case, a network functional entity known as Policy Control Function (PCF) constitutes the interface. Nevertheless, the interface may be provided directly between the network layers, that is between respective nodes thereof. In such a case, and with reference to the illustrated example, the interface would be provided between the Gateway GPRS Support Node GGSN and the Call State Control Function CSCF (sometimes also referred to as proxy-CSCF). The CSCF in turn is adapted to communicate or which communicates with other functional entities and elements of the IP network such as for example a home subscriber server HSS, etc. (not shown).
Upon a call, the user equipment communicates via a Packet Data protocol (PDP) context. For the PDP context, a radio bearer (RB) is established between the user equipment UE and a Node_B of a radio access network RAN of the GPRS/UMTS network layer. A Node_B corresponds to a base station in a GSM network. The Node_B is under control of a Radio Network Controller RNC which corresponds to a base station controller BSC in GSM. Of course, a radio access network generally comprises a plurality of Node_B elements. For simplicity of the drawings, however, only one Node_B has been illustrated. An example for such a radio access network is UTRAN (UMTS Terrestrial RAN).
The radio access network RAN as an example for the access network (a non-radio access network (that is wired/fixed access network is also conceivable) is connected to a core network CN. A core network denotes the part of the GPRS/UMTS network which is independent of the connection technology of the terminal UE. In the illustrated example, the core network is a GPRS (General Packet Radio Service) core network. The core network comprises a Serving GPRS Support Node (SGSN) and a Gateway GPRS Support Node GGSN, which nodes are known as such and a detailed description thereof is therefore not necessary.
It is assumed that the terminal and/or user equipment UE/MS communicating with/via the above briefly outlined communication network has subscribed to GPRS.
Such a GPRS subscription contains the subscription of one or more PDP addresses (Packet Data Protocol). Each PDP address is described by one or more PDP contexts in the terminal (UE and/or MS), the SGSN and the GGSN. Each PDP context may be associated with a TFT (Traffic Flow Template). At most one PDP context associated with the same PDP address may exist at any time with no TFT assigned to it. Every PDP context exists independently in one of two PDP states (active/inactive). The PDP state indicates whether data transfer is enabled for that PDP address (and TFT) or not. In case all PDP contexts associated with the same PDP address are deactivated, data transfer for that PDP address is disabled. All PDP contexts of a subscriber are associated with the same MM context (Mobility Management) for the IMSI (International Mobile Subscriber Identity) of that subscriber.
The inactive state characterizes the data service for a certain PDP address of the subscriber as not activated. The PDP context contains no routing or mapping information to process PDP PDUs (Protocol Data Units) related to said PDP address. No data can be transferred.
The terminal (UE and/or MS) initiates a transition from the inactive to the active state by initiating the PDP context activation procedure.
In the active state, the PDP context for the PDP address in use is activated in the terminal MS, the SGSN and GGSN. The PDP context contains mapping and routing information for transferring PDP PDUs for said particular PDP address between the terminal (MS) and the GGSN. The active PDP state is permitted only when the mobility management state of the subscriber is standby, ready, PMM-idle or PMM-connected. The lu interface radio access bearer (RAB) may or may not be established for an active PDP context.
An active PDP context for a terminal (MS) is transferred to inactive state when the deactivation procedure is initiated.
At call release of a call of a terminal having subscribed to a GPRS network and communicating with/via the network, there occur situations in which the call is terminated, but the PDP contexts are still active. In such a case, data packets may still be tried to be transmitted to or from the PDP address associated to the still active PDP context.
As the charging of a service for a subscriber may be based on the amount of data transmitted to and from him, or on the time during which the PDP context is active, such a situation is undesirable for a subscriber in that the subscriber will be charged for data services not actually used and/or received.
Also, as the GPRS network is only enabled to serve a limited number of subscribers, i.e. forward data to a limited number of addresses for which PDP contexts are in an active state, such a situation is undesirable in terms of a waste of communication network resources, as other subscribers could be blocked by active PDP contexts of subscribers no longer actually participating in a call.